Conduction electrons interact with localized electrons at the interface through an sd-exchange
potential [1]}, [2]}. Thus, the Hamiltonian is written as the sum
\(H=H^m+H^e+H^{sd}\) , where \(H^m\) , \(H^e\) , and \(H^{sd}\)  are the magnetic,
electronic, and interface contributions, respectively. The usual ferromagnetic Heisenberg model gives the magnetic Hamiltonian
\(H^m=-\frac{J}{2}\sum _{\langle ij\rangle }{\bf S}_i\cdot {\bf S}_j-g\mu _B\sum _i {\bf S}_i\cdot {\bf B}_i(t)\) 
